The present invention relates generally to the field of monostable multivibrator circuits and more particularly to the use of an improved diode feedback monostable multivibrator circuit in the ignition system of an internal combustion engine.
Monostable multivibrator circuits are well known to those of ordinary skill in the art and basically perform the function of responding to a trigger signal by producing an output pulse which has a predetermined duration. Typically, the monostable multivibrator responds to a predetermined polarity transition of the trigger signal and produces an output pulse which has a predetermined controllable duration. The term "pulse" as used herein, and as commonly used in the electronics industry, referes to a signal having abrupt (step) transitions. Thus a sine wave signal is not contemplated as being a pulse signal whereas a square wave signal does meet the definition.
Monostable multivibrators generally include input and output active devices. These devices have one inherently stable state and are triggered into a temporary unstable state in response to a trigger signal transition. The duration of the unstable state is determined by a timing capacitor and charging circuit which charge up the capacitor until a predetermined voltage threshold level is obtained, at which point the monostable reverts back to its stable state. One characteristic of such circuits is that a feedback connection is provided between one of the output terminals of the output device and a terminal of the input device. This feedback connection results in maintaining the input device in its unstable state, and thereby maintaining one terminal of the timing capacitor at a predetermined voltage level, during the duration of the monostable pulse. This prevents the monostable from responding to subsequent trigger signals which occur during the creation of the monostable pulse and prevents opposite polarity trigger signal transitions from disturbing the operation of the monostable circuit during the creation of the monostable output pulse. All of the above is well known to those of ordinary skill in the electronics art.
Monostable multivibrator circuits are generally used in electronic ignition systems for internal combustion engines. These circuits receive a timing signal from a cylinder position sensor and create predetermined variable or fixed width pulses in response thereto. These pulses are then used to control the spark timing and dwell characteristics of the electronic ignition system. One such electronic ignition system is illustrated in U.S. Pat. No. 3,933,141 to Philip Gunderson, which is assigned to the same assignee as the present invention.
In many monostable multivibrator circuit applications it is necessary to provide additional power gain stages subsequent to the monostable multivibrator. It is also occasionally desirable to provide for inverting the output signal produced by a basic two device monostable multivibrator. Thus in a great many applications, a basic two device monostable multivibrator is followed by additional stages of gain and inversion. The present invention basically deals with a novel electronic configuration in which the output of a subsequent inversion stage is fed back to the timing capacitor by a diode and thus eliminates the need for an input feedback device. This novel electronic configuration is illustrated as being adaptable for use in the electronic ignition system of an internal combustion engine.